Organic polymer coatings play a critical role in determining the overall performance of optical fibers. They protect the very fine silica glass fiber from abrasive damage and environmental effects, such as stress induced corrosion. In addition, they act as a buffer in reducing the sensitivity of the optical fiber to microbending loss. Stress induced corrosion by water is associated with stress concentrations at surface flaws under deformation. Regions of the surface of a glass fiber subject to contact with liquid water or water vapor at relatively high partial pressure are subject to surface hydrolysis of silicate bonds. These chemically damaged centers can act as nucleation sites for Griffith cracks which propagate with the local sound velocity into the interior of the fiber when subjected to external stresses. Polymer coatings for optical fibers must thus reduce permeation of water through the polymer matrix as well as reduce stress concentrations at surface flaws.